Chattanooga, Tenn, assignors to Combustion Engineering, Inc., Windsor, Court, a corporation of Delaware Filed Get. 11, 1962, Ser. No. 229,925 Claims. (Cl. 29-4573) The present invention relates to a novel method of bending tubes. In particular, the invention relates to a novel method for making a fitting comprising a pair of concentrically related tubes formed with a U-shaped return bend.

While it has particular application in the heat exchanger art where it is desired to effect a'return bend in a fitting comprising a reheater tube containing a concentric superheater tube, the present invention is applicable in most cases where it is desired to bend a plurality of concentrically arranged tubes simultaneously.

One method by which fittings of the instant type have been formed is as follows: first, the small inside tube is bent into a shape resembling a walking cane thereby making one leg of the element and the 180 return bend of the desired radius; secondly, a large outside tube is bent into an arcuate member of 180, and this member is fed around the 180 bendof the small tube. The other leg of the small tube is then hand welded to the cane, and a plurality of spacers are attached to the small tube at spaced positions along the two legs for centering the small tube inside the large tube. These spacers are positioned only along the straight portion of the element since there can be no spacers in the bend because of the ultimate expansion and contraction of the small tube. The two outer tube legs are lastly fed over the legs of the inner tube and Welded to the ends of the large 180 bend.

As can be readily seen, this method of forming the fitting is both cumbersome and time consuming involving many fabricating steps and a great amount of machining time. The result is a finished heat exchanger that is costly to produce.

By means of the present invention, this complicated, multistep process is replaced by a far simpler process which requires only the attachment of spacers along the small inner tube, the insertion of the inner tube within the outer tube, clamping the ends of the two tubes together and bending the two tubes simultaneously into-the desired shape by means of a conventional bending apparatus. Heat exchanger elements of the present type can now be made in much less time than those made by heretofore known methods, such as that described above, requiring only conventional equipment. The end result is aheat exchanger element which is much less expensive than those known to the art due to the decrease in manhours and fabricating steps required in forming the fitting.

It is, therefore, an object of the present invention to provide a novel method for fabricating heat exchanger elements comprising two concentrically arranged tubes.

It is also an object of the present invention to provide a novel method for bending two concentrically arranged tubes simultaneously and in a manner wherein the spacing between the two tubes is maintained.

With the foregoing and other objects in view, the invention comprises the novel method hereinafter more specifically described and illustrated in the accompanying drawings. However, it is to be understood that the invention comprehends changes, variations and modifications which come within the scope of the claims hereunto appended.

FIGURE 1 is a heat exchange element formed in accordance with the present invention.

3,253,325 Patented May 31, 1966 FIGURES 2-4 show the various stages of development of the element shown in FIGURE 1.

FIGURE 5 is a section of the element taken along 5-5 of FIGURE 3.

Referring now to the drawing, and more particularly to FIGURE 1 thereof, there is shown a heat exchange element 10 which has been fabricated in accordance with the teaching of the present invention. The element comprises a larger diameter outer tube 12 and a smaller diameter inner tube 14, which are concentrically arranged with respect to one another. The ends of the large tube 12 are capped by means of annular plates 11 which are apertured to receive the ends of the smaller tube 14. The plates 11 are welded to both of the tubes to thus define a pair of fluid-conducting passages through the element, one passage 13 extending through the smaller tube 14 and the other 15 being defined by the space between the two tubes. Spacers 16 serve to maintain the space between the two tubes and are positioned so as not to impede the flow of fluid through the passage 15, as shown in FIG- URE 5. Inlet means 17 and outlet means 19, in the form of short nipples communicating with the passage 15, are provided to permit the entry and exit of fiuid to and from the passage 15.

In fabricating the heat exchange element 10, there are first provided a pair of straight tubes 12 and 14, which are of different diameters. To the smaller diameter tube 14 are attached a plurality of spacer means to maintain the spacing between the two tubes when they are ultimately concentrically arranged, especially during the bending operation. Each of the spacer means consists of three spacer elements 16 spaced apart about the circumference of the tube and arranged in edgewise alignment with the longitudinal axis thereof. As shown in FIGURES 3 and 4, a set of spacers .16 are positioned on the tube 14 closely adjacent to those points which will be the tangent point between the bend and the legs of the element.

It must be noted that the spacers 16 are located such that they will lie only on the straight legs of the element leaving that portion which forms the bend free of such spacers so as to insure the unencumbered expansion and contraction of the tubes upon the admission of fluids of varying temperatures to the passages 13 and 15. To place spacers within the curved portion of the element would etiect points of stress at the locations of the spacers which would result in damage to the tubes.

After the spacers 16 have been attached to the tube 14, the .tube is telescopically inserted into the larger tube 12 with the ends of the tube 14 symmetrically projecting from either end of the tube 12. Clamping means are then applied to prevent any axial relative movement between the tubes during bending. This clamping means consists of a pair of annular, cup-shaped members 21) which are apertured to receive the ends of the smaller tube 14 and have a recess of a size capable of receiving the ends of the larger diameter tube 12, are placed in position upon each end of the assembly. Engaging elements, in the form of capscrews 22, are carried by the clamping members 20 and serve to anchor-the clamping means in position as shown, each clamping member 26 being provided with a plurality of capscrews 22, some of which engage the outer tube 12 and lock it within the clamping member recess and the others engaging the ends of the inner tube 14.

With the two tubes, 12 and 14, being assembled and clamped in place, the assembly can then be placed in any conventional bending apparatus which is capable of.

operating thereon and a bending force applied to the assembly to effect the bend and thus arrive at the final configuration, the bend in the embodiment shown being 180 in extent to arrive at a U-shaped heat exchanger element.

To eifect the simultaneous bending of the two tubes while insuring the maintenance of the spacing between the tubes throughout the extent, it is necessary that a set of spacers 16 be positioned closely adjacent to the tangent line 18 between the bend and the legs of the tubes. By so positioning the spacers, the two tubes become, in effect, clamped at the tangent line 18 thereby permitting the simultaneous bending of the tubes while maintaining the spacing between the inner and outer tubes throughout the length of the bend even in the absence of the presence of spacers therewithin.

The hereinabove invention permits the simultaneous bending of two tubes in a manner which is inexpensive and easy to perform. Moreover, it permits such bending by means of conventional bending apparatus without the need of expensive modification thereof.

The description set forth herein is intended to be merely illustrative of the invention and is not intended as a limitation thereto, it being understood that many and varied modifications can be made to the disclosed embodiment without departing from the spirit of the invention as defined by the appended claims. For example, bends other than 180 in extent may be formed in two concentrically arranged members without departing from the spirit of the invention.

What is claimed is:

1. The method of forming a bend in a plurality of concentrically related straight tubes of ditferent diameters comprising the steps of: bracing the tubes on that portion of the tube which will remain straight but closely adjacent the utimate point of tangency of the bend; assembling that tube within another tube of larger diameter; clamping the ends of said tubes against relative axial'movement; and bending the assembly to the desired degree.

2. The method of forming a bend in two concentrically related straight tubes of different diameters comprising the steps of: providing two straight tubes of determinant length and difierent diameters; bracing the tubes by attaching spacer means to the small diameter tube at longitudinally spaced positions along that portion of the tube which will remain straight but closely adjacent the ultimate points of tangency of the bend; assembling the smaller diameter tube within the larger diameter tube; clamping the ends of said tubes against relative axial movement and bending the assembly to the desired degree.

3. The method of fabricating a heat exchange element characterized by a pair of mutually isolated, fluid conducting passages formed by two tubes in concentric relation with one another and having a straight portion and an arcuate portion comprising the steps of providing.

two tubes of determinant length and different diameters; bracing the tubes by attaching spacer means including a plurality of circumferentially spaced spacer members to the smaller diameter tube at longitudinally spaced positions along that portion of the tube which will remain straight and closely adjacent to the ultimate points of tangency of the bend; assembling the smaller diameter tube within the larger diameter tube; clamping the ends of said tubes against relative axial movement; and bending the assembly to the desired degree.

4. The method of fabricating a heat exchange element characterized by a pair of mutually isolated, liquid conducting passages formed by two tubes in concentric relation with one another and having a straight portion and an arcuate portion comprising the steps of: providing two tubes of determinant length and different diameters; bracing the tubes by attaching spacer means including a plurality of radially projecting, circumferentially spaced spacer members to the smaller diameter tube at longitudinally spaced positions along that portion of the tube which will remain straight and closely adjacent to the ultimate points of tangency of the bend; assembling the smaller diameter tube within the larger diameter tube; clamping the ends of said tube against relative axial movement and bending the assembly to the desired References Cited by the Examiner UNITED STATES PATENTS 644,841 3/1900 Allen -l 29l57.3